diff options
Diffstat (limited to 'lispref/searching.texi')
| -rw-r--r-- | lispref/searching.texi | 35 |
1 files changed, 20 insertions, 15 deletions
diff --git a/lispref/searching.texi b/lispref/searching.texi index 336865c5642..7ba8a9fe666 100644 --- a/lispref/searching.texi +++ b/lispref/searching.texi @@ -231,11 +231,12 @@ this choice, the rest of the regexp matches successfully.@refill Nested repetition operators can be extremely slow if they specify backtracking loops. For example, it could take hours for the regular -expression @samp{\(x+y*\)*a} to match the sequence -@samp{xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxz}. The slowness is because -Emacs must try each imaginable way of grouping the 35 @samp{x}'s before -concluding that none of them can work. To make sure your regular -expressions run fast, check nested repetitions carefully. +expression @samp{\(x+y*\)*a} to try to match the sequence +@samp{xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxz}, before it ultimately fails. +The slowness is because Emacs must try each imaginable way of grouping +the 35 @samp{x}'s before concluding that none of them can work. To make +sure your regular expressions run fast, check nested repetitions +carefully. @item @samp{+} @cindex @samp{+} in regexp @@ -281,7 +282,7 @@ representations, because only the @sc{ASCII} characters are excluded. The beginning and end of a range must be in the same character set (@pxref{Character Sets}). Thus, @samp{[a-\x8c0]} is invalid because @samp{a} is in the @sc{ASCII} character set but the character 0x8c0 -(@samp{a} with grave accent) is in the Latin-1 character set. +(@samp{A} with grave accent) is in the Emacs character set for Latin-1. Note that the usual regexp special characters are not special inside a character alternative. A completely different set of characters are @@ -354,11 +355,11 @@ ordinary since there is no preceding expression on which the @samp{*} can act. It is poor practice to depend on this behavior; quote the special character anyway, regardless of where it appears.@refill -For the most part, @samp{\} followed by any character matches only -that character. However, there are several exceptions: two-character -sequences starting with @samp{\} which have special meanings. The -second character in the sequence is always an ordinary character on -their own. Here is a table of @samp{\} constructs. +For the most part, @samp{\} followed by any character matches only that +character. However, there are several exceptions: two-character +sequences starting with @samp{\} which have special meanings. (The +second character in such a sequence is always ordinary when used on its +own.) Here is a table of @samp{\} constructs. @table @samp @item \| @@ -393,8 +394,8 @@ or @samp{barx}. @item To enclose a complicated expression for the postfix operators @samp{*}, @samp{+} and @samp{?} to operate on. Thus, @samp{ba\(na\)*} matches -@samp{bananana}, etc., with any (zero or more) number of @samp{na} -strings.@refill +@samp{ba}, @samp{bana}, @samp{banana}, @samp{bananana}, etc., with any +number (zero or more) of @samp{na} strings. @item To record a matched substring for future reference. @@ -530,8 +531,8 @@ whitespace: @end example @end defun -@tindex regexp-opt @defun regexp-opt strings &optional paren +@tindex regexp-opt This function returns an efficient regular expression that will match any of the strings @var{strings}. This is useful when you need to make matching or searching as fast as possible---for example, for Font Lock @@ -555,8 +556,8 @@ regular expression which is equivalent to the actual value @end example @end defun -@tindex regexp-opt-depth @defun regexp-opt-depth regexp +@tindex regexp-opt-depth This function returns the total number of grouping constructs (parenthesized expressions) in @var{regexp}. @end defun @@ -1091,6 +1092,10 @@ subexpression is numbered 1, the second 2, and so on. Only regular expressions can have subexpressions---after a simple string search, the only information available is about the entire match. + A search which fails may or may not alter the match data. In the +past, a failing search did not do this, but we may change it in the +future. + @defun match-string count &optional in-string This function returns, as a string, the text matched in the last search or match operation. It returns the entire text if @var{count} is zero, |